Four of Antoni Gaudí’s masterpieces, walked in a single day, in the order a real visit took them. The route opens at the Sagrada Família, begun in 1882 and still unfinished, where flying buttresses give way to columns built like trees — the first slot of the morning is the one that beats the queues. It then drops to Passeig de Gràcia for two houses a few minutes apart: Casa Batlló, where Gaudí turned a sober apartment block into bone, water and scale, and Casa Milà, which Barcelona nicknamed the quarry as an insult and which has outlived the joke. The day ends uphill at Park Güell, a garden city almost nobody bought and which became the most joyful public park in the city. Six and a half kilometres, four buildings, one architect — and an argument about what a house is for.